Dryer apparatus for fiber webs

ABSTRACT

The invention relates to a dryer apparatus for fiber webs (10), such as webs of natural fiber, synthetic fiber and the like. The apparatus comprises a rotating dryer cylinder (1), the interior of which is provided with elements (8) for injecting hot heat-transfer fluid against the inner cylinder surface and for discharging if from the cylinder interior. The invention relates also to a method for heating a cylinder by injecting hot heat-transfer fluid against the inner surface of the heating cylinder.

BACKGROUND OF THE INVENTION

The present invention relates to a dryer apparatus for paper, cardboardor some other porous fiber web. The invention replaces thepressurized-steam heated cast-iron dryer cylinders available since thenineteenth century.

Development in the art of paper making machines has been slow andconcentrated mainly on the so-called wet end. An object of the machineis to dewater pulp pumped onto the machine and formed into an even fiberweb. As for a newsprint machine, for example, the dewatering breaks upas follows:

the wire section 98.8%, by suction and gravitation

the press section 0.6%, by pressing

the dryer section 0.6%, by steam-heated cylinders.

The dryer section constitutes about 80% of the total machine weight andalso represents technology from decades ago.

The dryer section of a paper machine, e.g. in the production ofcardboard and newsprint, comprises 45-65 cast-iron cylinders, diameter1.5-1.8 meters, fast rotating (peripheral speed 700-2000 meters/min.)pressure vessels. Carrying a fragile fiber web through such acomplicated installation without breaking the same and as required byquality standards is one of the most demanding challenges in papermaking. The dryer section also sets strict requirements for the buildingand subconstructions. Other factors adding to complexity include thepassage of a paper web, drive, machine ventilation, pocket ventilation,steam and condensate system, dryer felts, etc.

The "Yankee" cylinder is used for the manufacture of one side glazed(MG-) papers as well as cardboard and creped papers (tissue andindustrial crepes). It is a highly massive and demanding body ofcasting, having a diameter of 3-6 meters, a cylinder length of 3-6meters, and a weight of 50-100 tons with accessories. Heretofore, therehas been no viable, more preferred option available.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invented apparatus is to substantially simplify andimprove the drying of a paper web.

The invention is characterized in that the cylinder interior is fittedwith elements for the injection of a hot heat-transfer fluid against theinner surface of the cylinder for heating the surface, as well aselements for discharging the spent fluid from the cylinder interior,said cylinder being tight or sealed for eliminating fluid leaks.

In a preferred embodiment, the cylinder is provided with a dual-jacket,including an outer jacket against whose outer surface the web to bedried is laid, and the heat-transfer fluid injection elements anddischarge elements being positioned between said jacket surfaces.

In order to produce a preferred heating effect, the injection elementscan be directed towards an upper segment of the inner surface of theouter cylinder jacket and the discharge elements can be respectivelymounted on a lower segment within an intermediate space between thejackets.

The dryer cylinder rotates around a large-diameter stationary corecylinder and it is sealed e.g. with an anti-leak packing. The corecylinder may have a diameter which is e.g. 0.5-1.5 meters less than thatof the dryer cylinder.

In a preferred embodiment, the heating elements; and discharge elementsare stationary relative to the cylinder.

The drying cylinder can be at least partially covered by a drying hood,which is provided with an inlet and outlet duct for a drying medium,such as air, water vapor and/or an inert gas. In view of recoveringwaste heat, the inlet duct for a drying medium can preferably be in aheat-exchange contact with an inlet and/or outlet duct for aheat-transfer fluid, in addition to which the outlet duct for a dryingmedium can be fitted with a heat exchanger (13) for recovering its wasteheat, e.g. in view of heating water or air.

The present invention relates also to a method for drying fiber webs,such as webs of natural fiber, synthetic fiber and the like, by means ofa rotating, substantially horizontal cylinder, the fiber web to be driedbeing laid against the outer surface thereof. An essential feature inthe method is that the inner cylinder surface is injected or sprayedwith a hot heat-transfer fluid and that the spent heat-transfer fluid isdis-charged from the cylinder interior. This provides an effective heatexchange between the heat-transfer fluid and the cylinder surface to beheated. Temperature of the drying cylinder surface can be raised even toexceed 300° C., which is not possible by means of conventionalsteam-heated equipment.

The cylinder rotates on an assembly of supporting wheels and thecylinder is operated by means of a gear, a pinion, or a like drive wheelor wheel assembly in cooperation with the perimeter. The cylinderrotates around a fixedly mounted core cylinder. The core cylinder has adiameter of e.g. 1-5 meters and, thus, between the same and the rotatingcylinder surface remains a heating duct, the distance between thesurfaces being e.g. 0.3-1.0 meters. Hence, the cylinder core or centerdoes not rotate and, thus, in the cylinder heating duct, it is possibleto extend therethrough the supply and discharge pipes and the likeincluded in a heating system. The heating elements are immobile relativeto the rotating cylinder.

The core cylinder is mounted fixedly and propped against a framestructure standing on base tracks, such that the core cylinder remainsas an open space for the adjustment and maintenance of heatingequipment. The core cylinder is well insulated for eliminating heatlosses. There is a passage through the core cylinder even as the machineis running. A support and drive system for the dryer cylinder has beendescribed in Patent application No. 956213. In addition, in view ofstabilizing its rotation, the cylinder can be equipped with externalroller assemblies, which are mounted upon the core cylinder.

To improve the stability of the core cylinder, the end frame structurescan be connected by means of beam assemblies bracing the inner surfaceof the core cylinder. In order to compensate for thermal expansion ofthe core cylinder, one of the end rings of the cylinder is mounted onthe frame structure by means of a "slip joint".

The heat-transfer fluid may comprise a variety of liquids, such aswater, oil, or other appropriate fluids having a high thermal capacity.Preferred is a heat-transfer oil. All that is needed for heating acylinder surface with oil is an oil heating boiler with its accessories,supply ducts with nozzles therefor and, for recirculation, aconventional syphon generally used for condensate removal. Depending onits quality, oil is capable of providing a temperature of 300-500° C.,i.e. higher than conventional pressure steam.

The application of a large-diameter (1-5 meters) core cylinder of thisinvention offers a multitude of novel features, solutions, and benefits.

The horizontal cylinder rotates upon an assembly of supporting wheels.Optionally, the drive means may comprise a chain or a gearing, whereby agearing circles the periphery, and a motor-driven gear associatedtherewith. Of course, other per se known drive means can also be used,the essential feature being, however, that the drive is effected by wayof the cylinder periphery. A peripheral drive offers more accurate speedcontrol and lower energy consumption than a central drive.

The cylinders are principally made of steel plates, having a possiblethickness of 5-30 mm, the sheet being rolled and welded into a cylinderwhich can be turned, dressed and finished according to intended use. Thecylinder (i.e., annular) heating chamber is provided with fluid nozzlesand/or other accessories by bringing the same in by way of the corecylinder and through its shell. Between the end plate of the cylinderand the surface of the core cylinder is fitted a packing for eliminatingthe leak of a heat-transfer fluid. The rotating cylinder is furnishedwith internal reinforcement rings (e.g. 1.5-2.0 meters apart) forretaining the cylindrical shape.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference madeto the accompanying drawings, in which

FIG. 1 depicts a dryer cylinder apparatus of the invention,

FIG. 2 shows a cross-section of FIG. 1 along a line A--A, and

FIG. 3 shows an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 illustrate a horizontal metal cylinder 1 of the invention(FIG. 2 shows a cross-section of the apparatus shown in FIG. 1 along asectional line A--A). The cylinder 1 is mounted on a support frame 5. Adrying hood 7 (high velocity hood) encloses partially the cylinder 1,the bottom portion remaining outside the covering hood 7 for deliveringand discharging a fiber web. The drying hood can also be mounted alongthe sides or below the dryer cylinder.

The cylinder rests on top of supporting rolls 4, some of which areprovided with a drive and which, upon rotating against the periphery ofthe cylinder 1, rotate the cylinder. There may be a number of such drivewheels 4. A fiber web 10 to be dried is delivered onto the cylinder 1along a supply line which is guided by feed rolls as well as by a pressroll 3 pressing against the cylinder periphery. The fiber web can bebrought onto a drying surface e.g. by means of a so-called dryer felt.The fiber web can also be carried through drying between a felt and thecylinder surface. The support and drive wheels 4 are located on the sideperiphery of the cylinder so as not to touch the actual drying surfaceof the cylinder 1 and, thus, lie outside the working range of the pressroll.

The fiber web 10 to be dried is guided onto the surface of the cylinder1 to be carried thereby almost through a full revolution, whereafter itis removed e.g. by way of a guide roll 2 from the drum surface and thefiber web 10 is possibly guided further to a next dryer apparatus or awinding machine or the like.

The cylinder 1 is heated from inside by means of heating elements 8included in the interior thereof. The dryer cylinder 1 is heated frominside by means of hot-oil injection but, of course, a useful heatingfluid may be any one of a number of high-temperature boiling-pointheating fluids. The necessary heating elements are brought inside thedryer by way of a so-called core duct. The core duct is a cylinder,having a diameter of 1-5 meters, and it is fixedly propped against framestructures mounted on base tracks.

The cylinder can be made of steel plate with a thickness of 5-30 mm. Thesheet is rolled into a cylinder and the edges are welded. The dryercylinder can further be turned, dressed and finished according tointended use. Thus, the joints can be totally eliminated and the dryingresult is faultless.

The size of the dryer cylinder 1 is of course subject to intended useand it can be for example 1.5-7 meters in diameter and 2-10 meters inlength. In order to retain its shape, the cylinder is provided with anend plate as well as with reinforcement rings at appropriate spacings.The end plates may have a height of 0.3-1.0 meters and they extend tothe proximity (0.1-1.0 cm) of the jacket of the supporting cylinder.

The dryer cylinder 1 operates at normal atmospheric pressure and rotatesupon supporting rolls and it is rotated by means of the drive wheel 4running along its periphery or by means of a like drive means. Thus, theheating equipment can be mounted inside the cylinder in a stationarymanner.

For example, when drying newsprint or cardboard, it is possible to placeseveral, in an exemplary case 4-6, dryer units of the inventionsuccessively in such a geometry that results in a closed run for thefiber web.

In the embodiment shown in FIGS. 1 and 2, the cylinder comprises adual-jacket cylinder, the space between an outer jacket 1 and an innerjacket 11 accommodating heating-oil injecting nozzles 8. There is arelatively short distance between the cylinders, resulting in a smallheating chamber.

The oil is heated to a temperature of 300-500° C. with prior knowntechnology and it is pumped through an intake manifold internally of thecore cylinder to both transversely and longitudinally properly spacedheating-oil injection nozzles 8 for injecting the same against the innerwall of the dryer cylinder. The nozzles 8 can be adjusted and maintainedfrom inside the core cylinder even as the machine is running. Anadjustment of the injection nozzles nozzle 8 results in an adjustment oftemperature profile. Since the heating chamber remaining between thecylinders 1, 11 is limited and the core cylinder is effectively heatinsulated, the heat loss in a dryer of the invention is minimized. Thedryer cylinder 1 is subjected to the action of a centrifugal forceproduced by rotating motion so as to build a uniform layer of hot oil onthe inner cylinder surface. The thickness of such a layer is regulatedby means of a siphon 9, included in the bottom portion of the cylinderand normally used also in draining.

The high temperature of oil and its high transfer of heat to metalrender the solution of the invention more effective than conventionalhigh-pressure steam heating.

FIG. 2 refers to oil heating. A supply duct 12 is used for pumping hotoil inside the cylinder 1, which is injected by way of the nozzle 8 ontothe inner surface of the dryer cylinder in the top segment thereof. Theoil trickled to the bottom portion of the cylinder 1 is discharged e.g.by means of the prior known syphon 9 to a heating device, wherefrom itis delivered in a heated condition and e.g. through a heat exchanger 12,wherein drying air is heated, to a drying hood 7 and onto the outersurface of a fiber web lying on the outer surface of the cylinder 1. Themoist hot air emerging from the drying hood 7 is delivered to a secondheat exchanger 13, wherein the water vapor condenses and at the sametime the heat is transferred to water for further exploitation thereofin so-called pulp processing etc.

One significant benefit of the invention is that the apparatus andmethod can be applied and used very advantageously in already existinginstallations. FIG. 3 depicts a conventional cast-iron dryer cylinder 1rotating upon end bearings 15, originally intended to be heated bypressure steam. Inside such a tight cylinder is extended a heat-transferfluid supply pipe 8 with its nozzles. This supply pipe is journalled atone end to the back wall of the cylinder 1. In addition, into thecylinder is extended a heat-transfer fluid discharge pipe or siphon 9,provided with a syphon for sucking out the fluid collected an the bottomof the cylinder and for returning it to the fluid heater for itssubsequent recirculation as a hot heat-transfer fluid into the cylinder.According to the invention, it is possible to give up the use ofpressure in a dryer cylinder and to improve the heating effect by simplemeans and at very low costs.

The press roll 3 pressing a fiber web against the surface of the dryercylinder 1 applies a high external pressure to the cylinder 1. In orderto offset this, the interior of the cylinder 1 can be provided with acounter-roll (not shown) in alignment with the press roll 3 and adjacentto the siphon device 9. The counter-roll has its surface preferablyrecessed to form e.g. 10-50 mm deep and 10-50 mm wide grooves along theroll length. By virtue of the grooves, the heat-transfer fluid does notbuild in front of the counter-roll a layer of material affectingrotation of the cylinders and transfer of heat as the counter-rollrotates inside the cylinder. The counter-roll dimensioning is selectedaccording to the dryer cylinder and its design, a typical length is 3-8m and the diameter is less than the inner diameter of the dryercylinder. In addition to and as an alternative for an internalcounter-roll, it is possible to employ an external counter-roll which islocated on the cylinder surface opposite to the press roll 3. Positionedlike this, the counter-roll also presses the web 10 against the cylinder1.

The apparatus and method of the invention are applicable to the dryingof all types of fiber webs, such as paper, cardboard, pulp, syntheticfiber and the like webs. The method is also highly suitable for drying acoating and yields a high-quality finish.

What is claimed is:
 1. An apparatus for drying a fiber web, theapparatus comprising:a substantially horizontal, dual-jacket structurecomprising an outer rotatable cylinder and a stationary, non-rotatingcore disposed within the rotatable cylinder, wherein the core comprisesan inner jacket and the rotatable cylinder comprises an outer jacket;two end walls between the inner jacket and the outer jacket, comprisingan anti-leakage packing, whereby a space between an inner surface of theouter jacket and an outer surface of the inner jacket comprises a sealedheating chamber; wherein the non-rotating core comprises an open spacefor adjustment and maintenance; an assembly of support wheels externallysupporting the rotatable cylinder, the wheels including at least onedriving wheel rotating the rotatable cylinder; and fluid injectionelements directing a heat transfer medium onto an inner wall of theouter jacket for heating an outer surface of the rotatable cylinder,against which the web is to be dried, and discharge elements in thespace between the outer and inner surfaces of said jacket fordischarging spent heat transfer media from the interior of saidcylinder.
 2. The apparatus as set forth in claim 1, wherein the openspace comprises a passage running therethrough.
 3. The apparatus as setforth in claim 1, wherein the non-rotating core is insulated.
 4. Theapparatus as set forth in claim 1, wherein the discharge elementsextending through said end walls.
 5. The apparatus as set forth in claim1, wherein the fluid injection elements comprise outlets directedtowards an upper segment of the inner surface of the outer jacket ofsaid cylinder.
 6. The apparatus as set forth in claim 1, wherein thedischarge elements are mounted on a lower segment in the space betweenthe outer and inner jackets of said jacket.
 7. The apparatus as setforth in claim 1, wherein the fluid injection elements for the heattransfer media comprise outlets directed towards an upper segment of theinner surface of the outer jacket of said cylinder and the dischargeelements are mounted on a lower segment in the space between the outerand inner jackets of said jacket.
 8. The apparatus as set forth in claim1, wherein the non-rotating core is cylindrical and has a diameter 0.5 mto 1.5 m less than a diameter of said cylinder.
 9. The apparatus as setforth in claim 1, wherein said cylinder comprises rolled and weldedsteel plate which is turned and dressed.
 10. The apparatus as set forthin claim 1, wherein said cylinder is cast, turned, and dressed.
 11. Theapparatus as set forth in claim 1, comprising a drying hood comprisingan inlet duct for an additional drying medium selected from air, steam,an inert gas and mixtures thereof.